Noncorrosive heat-transfer liquid



Patented May 23, 1944 uui'reo STATE S PATENT; caries- 1' I 'amsss l NoNoonnosrvn nna'r-rmsm mourn tion of New York No Drawing. Application June a, 1940,

Y Serial No. 339,494

11 Claims.

The invention relates to new heat-transfer liquid compositions which have non-corrosive properties, and are especially adapted for use in the fluid cooling systems of internal combustion engines. It is particularly concerned with improved corrosion inhibitors for protecting the metals of a cooling system in contact with heattransfer liquids, including those composed of an alcohol as a freezing point depressant.

Alcohols are commonly used in anti-freeze cooling fluids, including both monohydric and polyhydric compounds, such as methanol, ethanol, propano'l, the glycols. polyglycols, and glycerol. The polyhydric alcoholsand their derivatives, sometimes in mixture with other high boiling, low freezing liquids have also been proposed as so-called high temperature coolants. The present invention, in its broadest aspect, is applicable to any of these heat-transfer fluids,

' both in aqueous solution or in concentrated form,

tors, are conducive to reactions which may cause metal corrosion. It has, therefore, become customary to add inhibitors to alcohol anti-freeze and high temperature coolants for the purpose of preventing orcounteracting induced corrosive conditions. Many materials have been proposed as additive inhibitor agents, but the need still exists for a more complete and satisfactory protection for all metals of a cooling system, which usually contains in its structure iron, brass, copper, solder and aluminum.

It is an object of this invention to provide improved corrosion inhibitors for heat-transfer liquids which will repress or prevent induced corrosive conditions, and more eifectively protect all metals of a cooling system. A further object is to provide improved heat-transfer-liquids, particularly those of an alcohol anti-freeze type, of more permanent non-corrosive properties.

We have found that silicic acid esters of monoh ydric and polyhydric alcohols exhibit as a class an excellent corrosion preventive action in alco. hol anti-freeze liquids and other cooling fluids, and will effectively protect all metals of the usual cooling system. Numerous compounds ar operative within the broader scope of the invention, including alkyl silicates, such as methyl silicate, ethyl silicate, butyl silicate, and army] silicate: aryl silicates, as represented by benzylsllicate; and various glycol and glycerol silicate ester derivatives. Effective inhibitor concentrations of these esters will vary with different heat-transfer compositions, but only small amounts are usually necessary, within a broad range of about 0.01% to 1.0% by weight 01 the concentrated alcohol or undiluted coolant, or more specifically from about 0.05% to 0.3% by weight.

While certain of the properties of the organosilicon esters are known, few of them are at present' available commercially, although sufliclent tests have been made to indicate clearly an inhibitor function in the entire group. Ethyl silicate, or more specifically tetraethyl ortho silicate, is probably better known than others of these compounds, and for that reason, as well as because of its excellent corrosion preventive action, is a preferred inhibitor. Tetraethylene glycol silicate is another specific compound equally effective to ethyl silicate. These esters exert their protective action in aqueous or non-aqueous cooling compositions, and in neutral or alkaline solutions. They have a tendency, however, to hydrolyze rapidly in water solutions, formin colloidal suspensions of a highly hydrated silicon compound, and this is of advantage in obtaining a most uniform distribution of the inhibitor. In alcohol cooling fluids, for example, the ester may be added to the concentrated alcohol, and upon dilution with water to form th usual anti-freeze composition, the hydrolyzed product becomes very uniformly distributed throughout the cooling fluid. Alkaline conditions will more readily promote this hydrolysis, and alkaline reacting materials, such as sodium hydroxide or triethanolamine, are therefore preferably added to an alcohol anti-freeze, in an amount suflicient to create a pH value of from about 9.0 to 12.0 in the cooling solution. Ethyl silicate is soluble in the concentrated monohydric alcohols, such as methanol and ethanol, and a particularly advantageous use of these inhibitors will thus be found in the volatile alcohol anti-freeze liquids. This does not, however, preclude the use of the compounds in glycols or their derivatives, and other high boiling, low freezing coolants, where the silicon ester may or may not be soluble. and

Provides eiiective metal protection either in the concentrated coolant, or as hydrolyzed in aqueous solutions.

The protective action of the new inhibitors rials, or anti-leak and'anti-i'oam agents. A speciflc formula containing additional inhibitor materials, which has .proven especially efl'ective in a cooling fluid containing methanol as the freezing point depressant, consists in percentage by weight of the alcohol or 0.3% sodium nitrite, 0.03% sodium nitrate, 0.075% sodium hydroxide. {and 0.1% tetraethyl ortho silicate. Another representative methanol anti-freeze coolant contains 0.20% ethyl silicate and 0.15% sodium 8- droxide, with no other additive corrosio inhibitor. In ethylene glycol cooling fluids of ethyl silicate as shown in the two above formulae give equally eflective corrosion protection, and similar quantities of tetraethylene glycol silicate are also suitable with any of the usual alcohol coolants, where again additional inhibitoragents may be added, ii desired.

Many variations in specific formulae will be evident, and for different alcohols 01' other coolants the preferred concentrations of the essential silicon ester inhibitor can be readily determined. Such modifications are intended to be included within the broader scope'of the invention. 'as are many different formulae in which other inhibitors may be employed along with the essential one of this disclosure.

We claim: I

' 1'. A non-corrosive heat-transfer liquid comprising an aqueous solution of an alcohol, and an inhibitor containing as the essential corrosilon preventive the hydrolyzed product of a silicic acid ester of a member of the group consisting of monohydric and polyhydric alcohols, said ester being present initially in the unhydrolyzed state in an amount not substantially greater than 1.0% by weight'oi' the alcohol in the heat-transfer liquid.

2. A non-corrosive heat-transfer liquid com ounts 4 amass" lysed state in an amount oi about 0.01% to 1.0%

by weight of the alcohol.

6. A non-corrosive heat-transfer liquid comprising an aqueous solution 01' an alcohol, and an inhibitor consisting essentially oi a mixture oi line component, the latter in suillcient amount to create a'pH value of from about 9.0 to 12.0.

6. A non-corrosive heat-transier liquid comprising an aqueous solution of a monohydric alcohol, and an inhibitor consisting essentially oi a mixture 01' the hydrolyzed product oi tetraethyl ortho silicate, sodium nitrite, sodium nie trate, and sodium hydroxide.

'l. A non-corrosive heat-transfer liquid comprising an aqueous solution oi methanol, and

an inhibitor consisting essentially oi a mixture of the hydrolyzed product oi'tetraethyl ortho silicate. said silicate being present initially in the unhydrolyzed state in an amount oi. about 0.1% by weight of the methanol, about 0.3% sodium nitrite, about 0.03% sodium nitrate, and about 0.075% sodium hydroxide.

8.. Method of inhibiting corrosion of metals by an aqueous alcohol cooling fluid in contact therewith, which comprises contacting said fluid with the-metal in the presence of an inhibitor containing as the essential corrosion preventive the hydrolyzed product of a silicic acid ester of a member of the group consisting of monohydric and polyhydric alcohols, said ester being present initially in the-unhydrolyzed state in an amount not substantially greater than 1.0% by weight of the alcohol in the cooling fluid.

9. Method oiinhibiting corrosion of metals by an aqueous alcohol cooling fluid in contact therewith, which comprises contacting; said fluid with the metal in the presence of aninhibitor containing as the essential'corrosion preventive the hydrolyzed products! a member of the group consisting oi ethyl silicate and tetraethylene glycol silicate, said silicate being present initially in the unhydrolyzed state in an prising an. aqueous solution of an alcohol, and an inhibitor containing as the essential corrosion preventive the hydrolyzed product of a silicic acid ester of a member oi the group consisting oi monohydric and polyhydric alcohols, said es- 'ter being present initially in the unhydrolyzed state in an amount of about 0.01% to 1.0% by 'i' weight of the alcohol in the heat-transfer liquid;

. 8. A non-corrosive heat-transfer liquid comprising an aqueous solution of an alcohol, and

an inhibitor containing as the essential corrosion ethylene glycol silicate, said tetraethylene glycol silicate being present initially in the unhydrolatter in suflicient amount to create a pH value of from about 9.0 to 12.0 in the cooling fluid.

' 11. Method of inhibiting corrosion of metals by an aqueous monohydric alcohol cooling fluid in contact therewith, which comprises contacting said fluid with the metal in the presence of an inhibitor consisting essentially of a mixture oi the hydrolyzed product oi tetraethyl ortho silicate, sodium nitrite, sodium nitrate. and sodium hydroxide. I

LEO J. CLAPSADLE. GORDON B. GRAHAM. 

